This invention generally concerns an apparatus suitable for use in melt processing and coextruding a variety of polymer resins. This invention particularly concerns a coextrusion feedblock suitable for use in conjunction with melt processing rigid vinyl chloride polymer resins. This invention more particularly concerns a modular coextrusion feedblock which, in conjunction with a conventional die, provides a maximum extruder head pressure of about 5000 pounds per square inch (psi) (34.5 megapascals (MPa)).
Coextrusion of sheet or film permits preparation of a wide variety of laminates by the simultaneous extrusion of two or more diverse thermoplastic materials. Many of these laminates contain several layers. One such laminate is disclosed in U.S. Pat. No. 3,524,795 (Peterson). Coextrusion apparatus used in preparing such laminates include that described in U.S. Pat. No. 3,924,990 (Schrenk), the teachings of which are incorporated herein by reference.
A coextrusion apparatus is generally designed for a specific product or combination of polymer resins. When one or more of the resins are halogenated resins, care must be taken to avoid conditions which promote dehydrohalogenation of the resin. Irrespective of the type of resin, pressure drop across a combination of a feedblock and an associated die should not be excessive if polymer leakage and machine damage are to be avoided. Pressure drop is sometimes referred to as pressure buildup or extruder head pressure. Potential machine damage includes, but is not limited to, excessive thrust bearing wear and destruction of screw flights on an extruder screw when an extruder is used to supply heat-plastified polymer to the apparatus.
It would be desirable if there were available an improved multiple extrusion feedblock suitable for extrusion of rigid vinyl chloride polymer compositions. Such a feedblock, in conjunction with an associated forming die, would beneficially have a maximum pressure buildup of 34.5 MPa.
It would also be desirable if there were available an improved multiple extrusion feedblock which permitted rapid cleaning thereof, particularly when such an apparatus includes one or more arcurate or nonlinear passageways having a length of about three inches (7.62 Centimeters) or more.
It would further be desirable if there were available an improved multiple extrusion apparatus which minimizes, if not eliminates, bolt stretching due to polymer migration at sealing surfaces.
It would still further be desirable if there were available an improved multiple extrusion apparatus which permitted rapid disassembly and reassembly in order to minimize downtime.